1. Field of the Invention
The present invention relates to multi-layer ceramic electronic parts having, for example, a laminated body of internal electrode patterns and ceramic layers therein, at end portions of which are provided external electrodes so as to connect to the internal electrodes, and in particular to multi-layer ceramic electronic parts in which a material common with a ceramic material for forming the ceramic layers of the laminated body is added into at least a portion of the external electrodes, and further a manufacturing method thereof.
2. Description of Related Art
As electronic components of a laminated type can be listed, for example, a laminated capacitor, a laminated inductor, a laminated piezo element, a laminated filter, a ceramic multi-layer circuit board, etc.
For example, in a laminated ceramic capacitor being the most representative one of the laminated electronic components, a large number of layers are stacked or laminated, each having an internal electrode and made of dielectric material, wherein the above-mentioned internal electrodes are pulled out to the end surfaces of the laminated body opposing to each other and, on the end surfaces to which those internal electrodes are pulled out, are formed external electrodes, and those external electrodes are connected to the above-mentioned internal electrodes, respectively.
The above-mentioned laminated body 3 of the laminated ceramic capacitor has a layer construction as shown in FIG. 3, for example. Namely, the ceramic layers 7, 7 . . . , each having the internal electrode 5 or 6 and made of dielectric material, are laminated in an order as shown in the FIG. 3, and further on both sides (i.e., upper and lower sides) thereof are stacked or laminated the ceramic layers 7, 7 . . . in a plurality thereof, on which no electrode 5 or 6 is formed, respectively. Upon the end portions of the laminated body 3 having such a layer structure therein, the internal electrodes 5 and 6 are exposed to one another, and as shown in FIG. 1, the above-mentioned external electrodes 2 and 2 are formed at the end portions of this laminated body 3.
Such a laminated ceramic capacitor, ordinarily, is not manufactured one by one, or in a unit of one part as shown in FIG. 3, but actually is obtained with a manufacturing method which will described below. Namely, first of all, minute ceramic powder and organic binder are mixed to prepare a slurry, and it is extended thinly on a carrier film made from a polyethylene terephthalate film, etc., by means of doctor blade method. Then, it is dried to be formed into a ceramic green sheet. Next, this ceramic green sheet is cut out into a desired size by a cutting head, while being mounted on the supporting sheet, and is printed with a conductive paste on one side surface thereof by a screen printing method, and is dried. With this, the ceramic green sheets 1a and 1b are obtained, on each of which plural sets of the internal electrode patterns 2a and 2b are aligned or arranged in the vertical and horizontal directions, as shown in FIG. 4.
Next, plural pieces of the ceramic green sheets 1a and 1b, each having the above-mentioned internal electrode patterns 2a or 2b thereon, are stacked or laminated, and further are stacked several pieces of the ceramic green sheets 1, 1 . . . having no internal electrode 2a or 2b, at the top and the bottom thereof. They are compressed together, thereby to form the laminated body. Here, the above ceramic green sheets 1a and 1b are stacked on one another, on which the internal electrode patterns 2a and 2b are shifted by half of the length in a longitudinal direction thereof. After that, this laminated body is cut out into a desired size, thereby to manufacture laminated raw chips, and those raw chip are baked. In this manner are obtained the laminated bodies as shown in FIG. 3.
Next, this baked laminated body 3 is applied with a conductor paste on both ends thereof and is baked, and on the surface of the baked conductive film is treated a plating, thereby completing the laminated ceramic capacitor formed with the external electrodes at both ends thereof, as shown in FIG. 1.
The multi-layer ceramic electronic part, such as the laminated ceramic capacitor mentioned above, is mounted on a circuit board and is soldered at the external electrodes 2 and 2 on both ends thereof on land electrodes of the circuit board.
However, such a laminated ceramic capacitor generates thermal stress within the laminated body 3 due to heat-shock when being soldered at the external electrodes thereof or due to change of a circumference temperature under the condition of use after the soldering. With this thermal stress, in particular in an end portion of the external electrodes 2 and 2 of the laminated body 3, can easily occur cracks. The cracks occurring in the laminated body 3 bring about a lowering in insulation due to invasion of moisture inside and a lowering in static capacitance due to discontinuity of the internal electrodes 5 and 6, thereby causing a low reliability thereof.
Such a thermal stress causing the cracks in the laminated body occurs due to the difference in the thermal expansion ratio between the ceramic material, which is a main ingredient of forming the laminated body 3, and the conductor which is a main ingredient of forming the external electrodes 2 and 2. Then, conventionally, a measure was taken, into the conductor paste for forming the external electrodes 2 and 2 is added the ceramic material of forming the ceramic layer 7 as a common material, thereby to make small the difference between the ceramic layer 7 and the external electrodes 2 and 2 in the physical properties, such as the thermal stress therein.
However, if the common material, i.e., the ceramic material for forming the ceramic layer 7, is put or added into the conductor paste for forming the external electrodes 2 and 2 much, stickiness or adhesiveness of the external electrodes 2 and 2 onto the external electrodes 5 and 6 comes to be inferior, i.e., connecting resistance therebetween becomes large and also the electric properties thereof are deteriorated. Further the stickiness or adhesiveness onto the solder or Sn plating is also deteriorated. As a result of this, solder wetability of the external electrodes 2 and 2 comes to be inferior, therefore mis-mounting easily occurs when mounting the multi-layer ceramic electronic part(s) on the circuit board.
An object, according to the present invention, for solving the problem in the conventional art mentioned above, is to provide a multi-layer ceramic electronic parts, wherein cracks in the laminated hardly occur due to the heat-shock accompanying a change of temperature under the conditions of being soldered and of use thereafter, and further the adhesiveness between the external and internal electrodes and the adhesiveness of solder onto the external electrode are superior, as well, thereby also being superior in soldering property with the external electrodes.
According to the present invention, for achieving the above-mentioned object, pillar-like ceramic portions 22 extending in a direction of thickness of a conductor film 21 are scattered in the conductor films 21 of the external electrodes 2 and 2. Each ceramic portion contains a material common to the ceramic material forming the ceramic layers 7 of the laminated body 3. Therefore, it has a strong bonding power onto the ceramic layers 7 of the laminated body 3. On the other hand, the conductor layer 21 has a strong bonding power onto the internal electrodes 5 and 6 of the laminated body 3, and shows a good adhesiveness onto a plating film 24 on the surface thereof. With the conductor films 21 and the ceramic portions 22 scattered therein complementing each other in the characteristics thereof, it is possible to ensure the bonding power of the external electrodes 2 and 2 at the end portions and the adhesiveness with the plating thereof, and also to prevent from occurring the cracks within the laminated body 3.
Namely, according to the present invention, there is provided a multi-layer ceramic electronic part, comprising:
a laminated body 3 in which a ceramic layer 7 and internal electrodes 5 and 6 are laminated one another; and
external electrodes 2 and 2 provided at end portions of the laminated body 3, in which the internal electrodes 5 and 6 oppose each other and reach to one of at least a pair of edges of the ceramic layer 7, thereby leading the internal electrodes 5 and 6 to one of the end surfaces of the laminated body 3 and connecting the internal electrodes 5 and 6 with the external electrodes 2 and 2, respectively. Wherein pillar-like ceramic portions 22, which are continuous in a direction of thickness of a conductor film 21 forming the external electrodes 2 and 2, are scattered in the conductor film 21.
The ceramic portions 22, containing the common material with the ceramic material forming the ceramic layers 7 of the laminated body 3, have a strong bonding power onto the ceramic layers 7 of the laminated body 3. Those ceramic portions 22 are formed so that they are continuous from an inner surface of the conductor film 21 of the external electrodes 2 and 2 where it is in close contact with a surface of the laminated body 3 up to an outer surface thereof.
According to the present invention, the conductor film 21 of the external electrodes 2 and 2 is made of at least one metal selected from a group of Ni, Cu, Ag, Pd and Agxe2x80x94Pd, and the external electrodes 2 and 2 are baked at the same time as the baking of the laminated body 3.
In the multi layer ceramic electronic part, since the ceramic portions 22, containing the so-called common material therein, shows a good adhesiveness onto the ceramic layers 7 at the end portions of the laminated body 3, the adhesiveness of the external electrodes 2 and 2 can be maintained at the end portions of the laminated body 3. However, the ceramic portions 22 are in a pillar-like shape and are scattered in the external electrodes 2 and 2, the external electrodes 2 and 2 do not adhere to the ceramic layers 7 at the end portions of the laminated body 3, but rather adhere in a spot-like manner. Therefore, when a change occurs in temperature, the thermal stress occurring within the laminated body 3 is released or mitigated, accompanying the thermal expansion and/or shrinkage of the conductor films 21 of the external electrodes 2 and 2, thereby hardly bringing about the cracks within the laminated body 3.
On the other hand, the conductor films 21 being formed to enclose around the ceramic portions 22 shows a good adhesiveness with the internal electrodes 5 and 6 at the end surfaces of the laminated body. With this, the contact resistance between the external electrodes 2 and 2 and the internal electrodes 5 and 6 comes to be small, and at the same time, it is also difficult to cause an exfoliation of the conductor films 21 from the end surfaces of the laminated body 3, in particular, from the internal electrodes 5 and 6.
Further, by baking the external electrodes 2 and 2 at the same time when the laminated body 3 is baked, i.e., the baking of the so-called common material, which is contained in the conductor paste for forming the conductor films 21 of the external electrodes 2 and 2, in other words, the baking of the material for forming the ceramic portions 22 of the external electrodes 2 and 2, is performed at the same time as the baking of the laminated body 3. Therefore the ceramic portions 22 of the external electrodes 2 and 2 and the ceramic layers 7 of the laminated body 3 are baked as one body to obtain a strong adhesiveness therebetween.
In addition, the adhesiveness of the plating on surface sides of the external electrodes 2 and 2 is also good, therefore forming a fine plating film thereon, thereby obtaining a good adhesiveness with the solder.
As is mentioned previously, with the multi-layer ceramic electronic part, according to the present invention, not only the adhesiveness between the external electrodes 2 and 2 and the internal electrodes 5 and 6 at the end surfaces of the laminated body 3, but also the adhesiveness between the external electrodes 2 and 2 and the ceramic layers 7 becomes good. Also, the adhesiveness of the plating of solder or Sn is good upon the surfaces of the external electrodes 2 and 2. As a result of this, the wetability with solder of the external electrodes 2 and 2 is also good, thereby obtaining a high strength in soldering when the component is mounted.
Furthermore, thermal stresses hardly occur accompanying a change of temperature, therefore the cracks do not occur within the ceramic layers 7.
Such a multi-layer ceramic electronic part, according to the present invention, is obtained by the following steps of:
preparing a unbaked laminated body 3;
applying and drying a conductor paste, into which is added a material common with a ceramic forming the ceramic layers 7 of the laminated body 3, on the edge portions of the unbaked laminated body 3;
forming the external electrodes 2 and 2 so that they connect with the internal electrodes 5 and 6 at the end surfaces of the laminated body 3, by baking the laminated body 3; and
completing the multi-layer ceramic electronic part.
As is mentioned previously, when baking the conductor paste containing the material common with the ceramic material for forming the ceramic layers 7 of the laminated body 3, due to bad wetability of the conductor powder with the ceramic particles when being melted within the conductor paste, the ceramic particles come together by themselves to form the ceramic portions 22 mentioned above, therefore they are scattered in the conductor films 21 of the external electrodes 2 and 2.